4_DWDM System Debugging 25p

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DWDM System DebuggingDWDM System Debugging

Purpose of system debugging

Optical power balancing calculation

Example

content

System DebuggingSystem Debugging

Purpose: To find out the best receiving power for the receiver

If the transmitter can load the optical signal to the system normally and the receiver can receive the signal in the normal range, the DWDM system will work without error codes.

The best receiving range of the receiver is the best working point to find.


Optical power balancing

calculation

Example

content

Optical power balancing calculationOptical power balancing calculation

1. Channel power difference

DWDM system is a multi-wave system, that is, there are more than one wave transmitted in the fiber hence we should ensure every single wave has the same/similar optical power.

Control the difference between any two waves to less than 4dB. The less difference the better.

It is the base of WDM system.


To control the difference between each OTUT output to less than 4dB.

For OTUT of ZXMP M900, the output is about -3dBm with input.

OTU1OTU1OTU1OTU1

┇Input

ch1

chN

ch1

chN

λ1

λn

OTUnOTUnOTUnOTUn

OM

UO

MU BABA LALA PAPA

OD

UO

DU

λ1

λn

OTU1OTU1OTU1OTU1

┇

OTUnOTUnOTUnOTUn

OutputλS λS λS λS


< 4dB, suppose that OMU has NO insertion loss

Pm = N*Pi (mW) 10logPm=10log (N*Pi) (dBm)

10log Pm = 10logN + 10logPi

OTU1OTU1OTU1OTU1

┇Input

ch1

chN

ch1

chN

λ1

λn

OTUnOTUnOTUnOTUn

OM

UO

MU BABA LALA PAPA

OD

UO

DU

λ1

λn

OTU1OTU1OTU1OTU1

┇

OTUnOTUnOTUnOTUn

Output

PmPi

λS λS λS λS


Commonly, for AWG OMU, the insertion loss is about 7dB and for Coupler OMU, the insertion loss is about 15dB.

While doing the system debugging, the insertion loss of OMU should be tested.

OMUoutput = 10logPm – insertion loss


2. Input optical power to the line and the max. output of OA

OA’s output is the input of line and each OA card has it max. output power. The optical power should be controlled to prevent non-linear phenomenon.

E.g. OBA 2520 – gain: 25dB, max. output: 20dBm


E.g. In a 32-wave system, only 5 waves are to be used, OBA: 2520

a. max. output of 32 waves of OBA: 20dBm (for 32 waves)

b. max. output of single wave

10logPi = 10logPm - 10logN = 20 - 10log32 = 5dBm

c. max. output of 5 waves

10logPm = 10logPi + 10logN = 5 + 10log5 = 12dBm

d. max. input of 5 waves

input = output - gain = 12 – 25 = -13dBm

OTU1OTU1OTU1OTU1

┇Input

ch1

chN

ch1

chN

λλ11

λλn n

OTUnOTUnOTUnOTUn

OM

UO

MU BABA LALA PAPA

OD

UO

DU

λλ11

λλn n

OTU1OTU1OTU1OTU1

┇

OTUnOTUnOTUnOTUnλsλs λsλs λsλs λsλs

Output


Compare the output of OMU and the max. input of OBA to decide whether an attenuator is needed or not.

OMUoutput – Attenuation + Gain = OBAoutput


3. Best receiving power of the receiver

OTU receiver type: PIN & APD

PIN: -18~0 dBm, best: -7 dBm

APD: -28~-8 dBm, best: -14dBm

In ZXMP M900 system, PIN is commonly used for OTUT and APD is commonly used for OTUR & OTUG


Suppose that ODU has NO insertion loss.

10logPi = 10logPm – 10logN

OTU1OTU1OTU1OTU1

┇Input

ch1

chN

ch1

chN

λλ11

λλn n

OTUnOTUnOTUnOTUn

OM

UO

MU BABA LALA PAPA

OD

UO

DU

λλ11

λλn n

OTU1OTU1OTU1OTU1

┇

OTUnOTUnOTUnOTUnλsλs λsλs λsλs λsλs

Output


Commonly, for AWG ODU, the insertion loss is about 7dB and for Grating ODU, the insertion loss is about 15dB.

While doing the system debugging, the insertion loss of ODU should be tested.

ODUoutput = 10logPi – insertion loss


Compare the ODU output and the best receiving power (-14dBm) of OTUR to decide whether it needs an attenuators or not.

If attenuators needs to be added, it is better to add it between OPA and ODU.l


4. Power balancing for OAD

The drop signal of OAD card is sent to OTUR, so it is the same calculation as #

3, considering the best receiving power of OTUR.

The output signal of OAD card consists of 2 parts: passing-through waves and

adding waves.


In Out

Drop Add

M1 M2

Attenuation

Pi_d

Pm_in

Pi_p

Pi_a

Pm_out

Attenuation Attenuation


Compare 10logPi_d and the best receiving power of OTUR to decide whether it needs an attenuators between OAD and OTUR.

Control the output of OAD to satisfy the optical power balance ( < 4dB).△

Then, compare the Pi_d and Pi_add to decide whether it needs an attenuators between M1 and M2 or between OTUT and OAD.


Optical power balancing

calculation

Example

content

OTU1OTU1OTU1OTU1

┇Input

ch1

ch5

ch1

ch5

λλ11

λλn n

OTUnOTUnOTUnOTUn

OM

U32

OM

U32

BABA PAPA

OD

U32

OD

U32

λλ11

λλn n

OTU1OTU1OTU1OTU1

┇

OTUnOTUnOTUnOTUnλsλs λsλs

Output

1620 1412

Line loss = 20dB

-3dBm APD

Insertion loss = 7dB Insertion loss = 7dB

ExampleExample

Only five (5) waves are used in the thirty two (32) wave system given above, determine the attenuators needed.

NOTE:log2 = 0.3, log5 = 0.7

ExampleExample

Answer

OMU – OBA: 1 dB attenuation

Before OPA: 2 dB attenuation

OPA – ODU: 4 dB attenuation

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4_DWDM System Debugging 25p